The research program is concerned with the development and parametric analysis of discrete trial, repeated measures procedures for the study of delayed matching and delayed response performance in animals, and with the utilization of these procedures for the isolation and measurement of drug effects on memory processes. The concepts used in the analysis are derived both from experiments on animal behavior and from human memory studies. Two broad classes of situational variables: (1) stimulus or sensitivity variables (e.g., fixed or variable intertrial interval duration, stimulus discriminability), and (2) response or bias variables (e.g., reinforcement magnitude, response "cost") will be compared with drug treatment for their effects on performance in the standard delayed response and delayed matching experiments. Interactions between drug effects and parametric variations of the stimulus sensitivity and response bias variables, individually or in combination, will be specifically investigated. Results will be relevant to the following theoretical or conceptual issues: separation of drug effects on "registration", "storage", and on input into and retrieval from storage; relations between sensitivity to stimuli, delay duration, memory, and drug-induced "disinhibition"; and role of proactive interference in the deterioration of memory over time. The concepts that emerge from these experiments will also be used to predict specific outcomes of delayed alternation experiments.